System, method, and computer-readable medium for user equipment handoff within an IP-femtocell network

ABSTRACT

A system, method, and computer readable medium for provisioning communication services by an IP-based femtocell network is provided. Service of a user equipment may be transferred from one femtocell to another femtocell via a femtocell handoff procedure. Femtocell systems of the femtocell network perform link quality measurements and may distribute the link quality measurements to neighbor femtocells. A femtocell system may periodically evaluate the link quality with the user equipment. If an evaluation is made that the user equipment needs to be transferred to another site, the servicing femtocell site may evaluate the most recent link quality measurements received from neighboring femtocell sites and select a femtocell site for handoff. In the event that the femtocell network is deployed in an area serviced by a macrocellular network, handoff routines may provide preference for transferring the user equipment to a target femtocell system rather than a macrocell site.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/969,889 entitled SYSTEM, METHOD, AND COMPUTER-READABLE MEDIUM FORUSER EQUIPMENT HANDOFF WITHIN AN IP-FEMTOCELL NETWORK filed on Aug. 19,2013, issued U.S. Pat. No. 9,191,948, issued Nov. 17, 2015, which is acontinuation of U.S. patent application Ser. No. 12/252,202 entitledSYSTEM, METHOD, AND COMPUTER-READABLE MEDIUM FOR USER EQUIPMENT HANDOFFWITHIN AN IP-FEMTOCELL NETWORK filed on Oct. 15, 2008, issued U.S. Pat.No. 8,532,054, issued Sep. 10, 2013, which claims priority to U.S.provisional patent application Ser. No. 61/003,151 entitled SIP-IOSADAPTER FUNCTION filed Nov. 15, 2007, the disclosure of each of which isincorporated in its entirety herein by reference.

FIELD OF THE INVENTION

The present invention is generally related to radio access technologiesand, more particularly, to mechanisms for Internet protocol (IP)provisioning of a femtocell radio access network.

BACKGROUND OF THE INVENTION

Contemporary cellular radio systems, or mobile telecommunicationsystems, provide an over-the-air interface to wireless user equipments(UEs) via a radio access network (RAN) that interfaces with at least onecore network. The RAN may be implemented as, for example, a CDMA2000RAN, a Universal Mobile Telecommunications System (UMTS) RAN, a GlobalSystem for Mobile communications (GSM) RAN, or another suitable radioaccess network implementation. A UE may comprise, for example, a mobileterminal such as a mobile telephone, a laptop computer featuring mobiletelephony software and hardware, a personal digital assistant (PDA), orother suitable equipment adapted to transfer and receive voice or datacommunications with the radio access network.

A RAN covers a geographical area comprised of any number of cells eachcomprising a relatively small geographic area of radio coverage. Eachcell is provisioned by a cell site that includes a radio tower, e.g., abase transceiver station (BTS), and associated equipment. BTSscommunicate with UEs over an air interface within radio range of theBTSs.

Numerous BTSs in the RAN may be communicatively coupled to a basestation controller, also commonly referred to as a radio networkcontroller (RNC). The BSC manages and monitors various system activitiesof the BTSs serviced thereby. BSCs are coupled with at least one corenetwork.

BTSs are typically deployed by a carrier network in areas having a highpopulation density. The traffic capacity of a cell site is limited bythe site's capacity and affects the spacing of cell sites. In suburbanareas, sites are often up to two miles apart, while cell sites deployedin dense urban areas may be as close as one-quarter of a mile apart.Because the traffic capacity of a cell site is finitely limited, as isthe available frequency spectrum, mobile operators have a vestedinterest in technologies that allow for increased subscriber capacity.

A microcell site comprises a cell in a mobile phone network that coversa limited geographic area, such as a shopping center, hotel, airport, orother infrastructure that may have a high density mobile phone usage. Amicrocell typically uses power control to limit the radius of themicrocell coverage. Typically a microcell is less than a mile wide.

Although microcells are effective for adding network capacity in areaswith high mobile telephone usage, microcells extensively rely on theRAN, e.g., a controlling BSC and other carrier functions. Becausecontemporary BSCs have limited processing and interface capacity, thenumber of BTSs—whether microcell BTSs or typical carrier BTSs—able to besupported by the BSC or other RAN functions is disadvantageouslylimited.

Contemporary interest exists in providing enterprise and office access,including small office/home office (SOHO) radio access, by an evensmaller scale BTS. The radio coverage area of such a system is typicallyreferred to as a femtocell. In a system featuring a femtocell, a UE maybe authorized to operate in the femtocell when proximate the femtocellsystem, e.g., while the UE is located in the SOHO. When the UE movesbeyond the coverage area of the femtocell, the UE may then be servicedby the carrier network. The advantages of deployment of femtocells arenumerous. For instance, mobile users frequently spend large amounts oftime located at, for example, home, and many such users rely extensivelyon cellular network service for telecommunication services during thesetimes. For example, a recent survey indicated that nearly thirteenpercent of U.S. cell phone customers do not have a landline telephoneand rely solely on cell phones for receiving telephone service. From acarrier perspective, it would be advantageous to have telephone servicesprovisioned over a femtocell system, e.g., deployed in the user's home,to thereby reduce the load, and effectively increase the capacity, onthe carrier RAN infrastructure. However, due the large potential demandfor femtocell systems, contemporary BTS interface mechanisms with a RANvia BSCs or equivalent RNCs is impractical due to scaling issues.

Therefore, what is needed is a mechanism that overcomes the describedproblems and limitations.

SUMMARY OF THE INVENTION

The present invention provides a system, method, and computer readablemedium for provisioning communication services by an IP-based femtocellnetwork. An authorized user equipment may be serviced by the femtocellnetwork, and service may be transferred from one femtocell to anotherfemtocell via a femtocell handoff procedure. Femtocell systems of thefemtocell network perform link quality measurements and may distributethe link quality measurements to neighbor femtocells. A femtocell systemwith which a user equipment is registered may periodically evaluate thelink quality with the user equipment. If an evaluation is made that theuser equipment needs to be transferred to another site, the servicingfemtocell site may evaluate the most recent link quality measurementsreceived from neighboring femtocell sites and select a femtocell sitefor handoff. In the event that the femtocell network is deployed in anarea serviced by a macrocellular network, handoff routines may providepreference for transferring the user equipment to a target femtocellsystem rather than a macrocell site. In the event that a suitablefemtocell is unavailable for handoff of the user equipment, the userequipment may be transferred to the macrocell site.

In one embodiment of the disclosure, a method for providingcommunication services to a user equipment is provided. The methodcomprises communicatively coupling a plurality of femtocell systems witha packet-switched backhaul, registering the user equipment with a firstfemtocell system of the plurality of femtocell systems, measuring afirst radio interface quality between the user equipment and the firstfemtocell system, measuring a second radio interface quality between theuser equipment and a second femtocell system, transmitting an indicationof the second radio interface quality from the second femtocell systemto the first femtocell system, and invoking a handoff procedure from thefirst femtocell system to the second femtocell system.

In another embodiment of the disclosure, a computer-readable mediumhaving computer-executable instructions for execution by a processingsystem, the computer-executable instructions for providing communicationservices to a user equipment is provided. The computer-readable mediumcomprises instructions for communicatively coupling a plurality offemtocell systems with a packet-switched backhaul, registering the userequipment with a first femtocell system of the plurality of femtocellsystems, measuring a first radio interface quality between the userequipment and the first femtocell system, measuring a second radiointerface quality between the user equipment and a second femtocellsystem, transmitting an indication of the second radio interface qualityfrom the second femtocell system to the first femtocell system, andinvoking a handoff procedure from the first femtocell system to thesecond femtocell system.

In a further embodiment of the disclosure, a system for providingcommunication services to a user equipment is provided. The systemcomprises a packet-switched network having a domain with which the userequipment has a session initiation protocol service subscription, anInternet Protocol multimedia subsystem communicatively interfaced withthe packet-switched network, and a femtocell network including aplurality of femtocell systems communicatively coupled with thepacket-switched network. Each of the femtocell systems is adapted toprovide a radio interface with the user equipment. The femtocell networkincludes a first femtocell system with which the user equipment isregistered and that measures a first radio interface quality between theuser equipment and the first femtocell system. A second femtocell systemof the femtocell network measures a second radio interface qualitybetween the user equipment and the second femtocell system and transmitsan indication of the second radio interface quality to the firstfemtocell system. A handoff procedure is invoked to transfer servicefrom the first femtocell system to the second femtocell system. Thesecond femtocell system allocates a session initiation protocol useragent for the user equipment and submits a registration to a locationservice on behalf of the user equipment.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures, in which:

FIG. 1 is a diagrammatic representation of a network system thatincludes a cellular network adapted to provide macro-cellular coverage;

FIG. 2 is a diagrammatic representation of a conventional network systemconfiguration featuring a femtocell;

FIG. 3 is a diagrammatic representation of a network system in which afemtocell system implemented in accordance with an embodiment of thepresent invention may be deployed;

FIG. 4A is a simplified diagrammatic representation of femtocell systemdepicted in FIG. 3 that may be connected with an IP backhaul inaccordance with an embodiment;

FIG. 4B is a simplified diagrammatic representation of an alternativeembodiment of a femtocell system that may be connected with an IPbackhaul;

FIG. 5 is a diagrammatic representation of an exemplary sessioninitiation protocol registration message generated by a femtocell systemon behalf of a user equipment in accordance with an embodiment;

FIG. 6 is a diagrammatic representation of a network system featuring afemtocell network implemented in accordance with an embodiment;

FIG. 7 is a flowchart depicting a handoff routine for transfer of a userequipment from one femtocell system to another femtocell system inaccordance with an embodiment;

FIG. 8 is a flowchart depicting a handoff routine that facilitatestransfer of a user equipment from one femtocell system to anotherfemtocell system in accordance with an embodiment; and

FIG. 9 is a diagrammatic representation of a registration message thatmay be submitted to a location service by a target femtocell system towhich a user equipment is transferred during a handoff procedure inaccordance with an embodiment.

DETAILED DESCRIPTION OF THE INVENTION

It is to be understood that the following disclosure provides manydifferent embodiments or examples for implementing different features ofvarious embodiments. Specific examples of components and arrangementsare described below to simplify the present disclosure. These are, ofcourse, merely examples and are not intended to be limiting.

FIG. 1 is a diagrammatic representation of a network system 100 thatincludes a cellular network 110 adapted to provide macro-cellularcoverage to a user equipment. Cellular network 110 may comprise, forexample, a code-division multiple access (CDMA) network, such as aCDMA-2000 network.

Cellular network 110 may include any number of base transceiver stations(BTSs) 112 a-112 c communicatively coupled with a base stationcontroller (BSC) 114 or RNC. Each individual BTS 112 a-112 c under thecontrol of a given BSC may define a radio cell operating on a set ofradio channels thereby providing service to a user equipment (UE) 125,such as a mobile terminal. BSC 114 manages the allocation of radiochannels, receives measurements from mobile terminals, controlshandovers, as well as various other functions as is understood. BSC 114is interconnected with a mobile services switching center (MSC) 116 thatprovides mobile terminal exchange services. BSC 114 may be additionallycoupled with a packet data serving node (PDSN) 118 or other gatewayservice that provides a connection point between the CDMA radio accessnetwork and a packet network, such as Internet 160, and providesmobility management functions and packet routing services. MSC 116 maycommunicatively interface with a circuit switched network, such as thepublic switched telephone network (PSTN) 150, and may additionally becommunicatively coupled with an interworking function (IWF) 122 thatprovides an interface between cellular network 110 and PSTN 150.

System 100 may also include a signaling system, such as a signalingsystem #7 (SS7) network 170. SS7 network 170 provides a set of telephonysignaling protocols which are used to set up the vast majority of theworld's PSTN telephone calls. SS7 network 170 is also used in cellularnetworks for circuit switched voice and packet-switched dataapplications. As is understood, SS7 network 170 includes varioussignaling nodes, such as any number of service control points (SCPs)172, signal transfer points (STPs) 174, and service switching points(SSPs) 176.

BTSs 112 a-112 c deployed in cellular network 110 may service numerousnetwork 110 subscribers. Cell cites provided by BTSs 112 a-112 ccommonly feature site ranges of a quarter to a half mile, e.g., indensely populated urban areas, to one to two miles in suburban areas. Inother remotely populated regions with suitable geography, site rangesmay span tens of miles and may be effectively limited in size by thelimited transmission distance of relatively low-powered UEs. As referredto herein, a cell provided by a BTS deployed in carrier network 110 foraccess by any authorized network 110 subscriber is referred to as amacrocell.

FIG. 2 is a diagrammatic representation of a conventional network system200 configuration featuring a femtocell. In the depicted example, acentral BSC 214 deployed in a cellular carrier network 210 may connectwith a soft switch core 212 that is connected with a MSC 216. MSC 216connects with the cellular core network and may interface with othernetworks, such as the PSTN as is understood. BSC 214 may be connectedwith and service numerous BTSs 212 a-212 c that provide macrocells tocellular network 210 subscribers.

BSC 214 may additionally connect with a tunnel gateway system 218 thatis adapted to establish secured tunnels 232 a-232 x with respectivefemtocell systems 250 a-250 x. Femtocells comprise cellular accesspoints that connect to a mobile operator's network using, for example, aresidential DSL or cable broadband connection. Femtocells 250 a-250 xprovide a radio access point for UE 225 when the UE is within range of afemtocell system with which the UE has authorized access. For example,femtocell system 250 a may be deployed in a residence of the user of UE225. Accordingly, when the user is within the residence, mobiletelecommunications may be provided to UE 225 via an air-interfaceprovided by femtocell system 250 a. In this instance, UE 225 iseffectively offloaded from the macro BTS, e.g., BTS 212 a, andcommunications to and from the UE are carried out with femtocell system250 a over Internet 260. Thus, femtocell systems 250 a-250 x may reducethe radio resource demands by offloading UEs from macrocells tofemtocells and thereby provide for increased subscriber capacity ofcellular network 210.

In contemporary implementations such as that depicted in FIG. 2, afemtocell system 250 a comprises a transceiver without intelligence andis thus required to be connected and managed by BSC 214. Thus, femtocellsystems 250 a-250 x are reliant on the carrier network centralized BSC214 which has limited capacity and thus does not exhibit desirablescaling characteristics or capabilities. Moreover, high communicationsoverhead are realized by the BTS backhaul.

FIG. 3 is a diagrammatic representation of a network system 300 in whicha femtocell system implemented in accordance with an embodiment of theinvention may be deployed. System 300 includes a radio access network(RAN) 310 that provides an over-the-air interface with a UE 325, e.g., amobile terminal. RAN 310 may comprise, for example, a CDMA radio accessnetwork or another suitable RAN. RAN 310 may comprise various BTSs andassociated base station controllers BSCs as well as other infrastructureas is understood. UE 325 may be implemented as a personal digitalassistant (PDA), a mobile phone, a computer, or another device adaptedto interface with RAN 310.

System 300 may include an IP Multimedia Subsystem (IMS) 320 architectureadapted to provide IP service to UE 325. To this end, RAN 310 iscommunicatively coupled with a serving general packet radio service(GPRS) support node (SGSN) 314 and a gateway GPRS support node (GGSN)316. SGSN 314 provides the delivery of data packets from and to UE 325within its service area. GGSN 316 provides an interface between the GPRSbackbone network and external packet data networks. GGSN 316 iscommunicatively coupled with a policy decision function (PDF) 318 thatprovides authorization of media plane resources, e.g., quality ofservice (QoS) authorizations, policy control, bandwidth management, andthe like. PDF 318 may be communicatively coupled with a call sessioncontrol function (CSCF) 320.

CSCF 320 comprises various session initiation protocol (SIP) servers orproxies that process SIP signaling packets in IMS 320. CSCF 320 mayinclude a proxy-CSCF (P-CSCF) that provides a first point of contact foran IMS-compliant UE. The P-CSCF may be located in the visited network,or in the UE's home network if the visited network is not fullyIMS-compliant. UE 325 may discover the P-CSCF, e.g., by using DynamicHost Configuration Protocol (DHCP), or by assignment in a packet dataprotocol (PDP) context. CSCF 320 additionally includes a Serving-CSCF(S-CSCF) that comprises the central node of the signaling plane. TheS-CSCF comprises a SIP server, but additionally performs sessioncontrol. The S-CSCF is located in the home network and interfaces with ahome subscriber server (HSS) 340 to download and upload user profiles.CSCF 320 further includes an Interrogating-CSCF (I-CSCF) that comprisesa SIP function located at the edge of an administrative domain. TheI-CSCF has an IP address that is published in the Domain Name System(DNS) 372 that facilitates location of the I-CSCF by remote servers.Thus, the I-CSCF is used as a forwarding point for receipt of SIPpackets within the domain.

HSS 340 comprises a user database that supports the IMS network entitiesthat manage calls. HSS 340 stores user profiles that specifysubscription-related information of authorized users, authenticates andauthorizes users, and provides information about the user's physicallocation. Various application servers (AS) 342 a-342 n that host andexecute services interface with CSCF 320 via SIP.

CSCF 320 is coupled with a breakout gateway control function (BGCF) 322that comprises a SIP server that provides routing functionality based ontelephone numbers. BGCF 322 is used when a UE places a call from the IMSto a phone in a circuit switched network, e.g., PSTN 330, or the publicland mobile network. A media gateway controller Function (MGCF) 324performs call control protocol conversion between SIP and ISDN User Part(ISUP) and interfaces with a signaling gateway (SGW) 326. SGW 326interfaces with the signaling plane of a circuit switched network, e.g.,PSTN 330. SGW 326 may transform lower layer protocols, such as StreamControl Transmission Protocol (SCTP), into the Message Transfer Part(MTP) protocol, and pass ISUP data from MGCF 324 to PSTN 330 or anothercircuit switched network. A media gateway (MGW) 328 interfaces with themedia plane of PSTN 330 or another circuit switched network byconverting data between real-time transport protocol (RTP) and pulsecode modulation (PCM), and may also be employed for transcoding when thecodecs of the IMS and circuit switched networks differ. Resources of MGW328 are controlled by MGCF 324. Fixed access, e.g., IP telephony devices374 a-374 b, may connect with IMS network via Internet 370 that iscommunicatively coupled with IMS network 320 by way of border gateway360.

As is understood, DNS 372 comprises a scalable namespace thatfacilitates access to entities deployed on the Internet or privatenetworks. DNS 372 maintains various records for host names, servers, andthe like. For example, DNS 372 maintains records (commonly referred toas “A records”) that map hostnames to IP addresses, pointer (PTR)records that map IP addresses to canonical names to facilitate reverseDNS lookups, service (SRV) records that specify information on availableservices, naming authority pointer (NAPTR) records that facilitateregular expression based rewriting, and various other records. DNS 372may additionally include a telephone number mapping (ENUM) system thatfacilitates resolution of SIP addresses from E.164 number as isunderstood.

A base station manager (BSM) 378 may be deployed in Internet 370 and maybe adapted to communicate with numerous femtocell systems and femtocellnetworks. BSM 378 may provide various operations, maintenance, andmanagement functions to femtocell systems. For example, BSM 378 mayprovide service provisioning of femtocell systems, e.g., by providingconfiguration downloads to femtocell systems and preloading defaultconfiguration data for femtocell systems distributed via sales channels.BSM 378 may provide various support and maintenance features, such asalarm and periodic statistics reporting, automatic remote software imagedistribution to femtocell system, provide upgrades and reconfigurations,and may provide remote access via Internet 370 for diagnostics andcustomer support.

In accordance with an embodiment, a femtocell system 350 may includeintegrated BTS and BSC (and/or radio node (RN) and radio networkcontroller(RNC)) functions and may feature additional capabilitiesavailable in the provided femtocell site coverage area. Femtocell system350 provides an IP-accessible radio access network, is adapted foroperation with IMS 320, and provides radio link control functions.Femtocell system 350 may be communicatively coupled with Internet 370via any variety of backhaul technologies, such as an 802.11x link, a10/100 BaseT LAN link, a T1/E1 Span or fiber, cable set top box, DSLmodem connected with a central office digital subscriber line accessmultiplexer, a very small aperture terminal (VSAT), or another suitablebackhaul infrastructure.

In an embodiment, femtocell system 350 includes a session initiationprotocol (SIP) adapter that supports a SIP client pool and providesconversion of call set-up functions to SIP client set-up functions. Forexample, a SIP client pool allocated by femtocell system 350 maycomprise a plurality of SIP user agents 352 a-352 c that each may beallocated for a UE authorized to access femtocell system 350.Additionally, femtocell system 350 includes electronic serial number(ESN), and/or Mobile Equipment Identifier (MEID) screening, screening toallow only designated UEs to access the femtocell thereby restrictingaccess to authorized home or small office UEs. For example, femtocellsystem 350 may be configured with an ESN and/or MEID list 354 thatspecifies ESNs or MEIDs of UEs authorized to access femtocell system350. In the illustrative example, ESNs of “ESN 1”-“ESN 3” are includedin ESN list 354. Provisioning of ESN(s) or MEIDs may be made as part ofan initial femtocell system 350 activation. In the illustrative example,femtocell system 350 is allocated an Internet Protocol (IP) address of“66.249.73.42”, and UE 325 is allocated a mobile services ISDN (MSISDN)number, or E.164 number, of “12145551212”.

FIG. 4A is a simplified diagrammatic representation of femtocell system350 depicted in FIG. 3 that facilitates provisioning of a femto-RAN inaccordance with an embodiment. Femtocell system 350 includes an antenna400 coupled with a BTS 410. BTS 410 may be implemented, for example, asa 1×RTT ASIC device and may comprise a non-diversity receiver featuringa built-in duplexer. In an embodiment, BTS 410 may feature only oneoperational band and may include a transmitter scan receiver and localoscillator. BTS 410 may be communicatively coupled with a BSC 420 thatprovides radio control functions, such as receiving measurements fromUEs, such as mobile phones, control of handovers to and from otherfemtocell systems, and may additionally facilitate handoff to or frommacrocells.

Femtocell system 350 includes an electronic serial number screeningfunction 430 that may facilitate approving or rejecting service for a UEby femtocell system 350. Additionally femtocell system 350 includes anInternet Operating System (IOS) and SIP Adapter (collectively referredto as IOS-SIP Adapter 440). IOS-SIP adapter 440 may invoke and manageSIP clients, such as a user agent (UA) pool comprising one or more UAs.In accordance with an embodiment, each UE 325 authorized to be servicedby femtocell system 350 may have a UA allocated therefor by femtocellsystem in a manner that facilitates transmission of communications toand from a UE over an IP backhaul. Accordingly, when an authorized UE iswithin the femtocell system 350 site range, telecommunication servicesmay be provided to the UE via the IP backhaul and femtocell system 350provisioned RAN. When the UE is moved beyond the service range offemtocell system 350, telecommunication service may then be provided tothe UE via macrocellular coverage.

To facilitate routing of calls from circuit switched call originators,femtocell system 350 may perform a DNS/ENUM registration on behalf ofUEs authorized to obtain service from femtocell system 350. In thepresent example, assume UE 325 with a MSISDN of “12145551212” has a SIPservice subscription in the domain “example.com” and has a SIP uniformresource identifier (URI) of “12145551212@example.com”. An exampleDNS/ENUM registration message generated by femtocell system 350 onbehalf of UE 325 and transmitted to DNS 372 is as follows:

$ORIGIN 2.1.2.1.5.5.5.4.1.2.1.e164.arpa.

IN NAPTR 100 10 “u” “E2U+sip”

“!^.*$!sip:12145551212@example.com!”.

As is understood, the first line of the registration message comprisesthe MSISDN number of the UE converted (i.e., reversed with each numeraldelineated with a “.” character and appended with the e164.arpa domain)for DNS lookup. The second line of the registration message specifiesthe NAPTR record for the hosts that can further process the address—thedomain “example.com” (in which the UE with a URI of12145551212@example.com is registered) in the present example.

In accordance with another embodiment, femtocell system 350 may generateand issue a SIP registration on behalf of UE 325 authorized for serviceaccess by femtocell system 350.

FIG. 4B is a simplified diagrammatic representation of an alternativefemtocell system 450 that facilitates provisioning of a femto-RAN inaccordance with an alternative embodiment. Femtocell system 450 includesan antenna 400 coupled with a radio node (RN) 411. RN 411 may beimplemented, for example, as a 1×EV-DO ASIC device. For example, RN 411may provide a 1×EV-DO Rev. 0 air interface or a 1×EV-DO Rev. A airinterface. RN 411 may be communicatively coupled with a radio networkcontroller (RNC) 421 that provides radio control functions, such asreceiving measurements from UEs, control of handovers to and from otherfemtocell systems, and may additionally facilitate handoff to or frommacrocells. RNC 421 may also provide encryption/decryption functions,power, load, and admission control, packet scheduling, and various otherservices.

Femtocell system 450 includes an electronic serial number screeningfunction 430 that may facilitate approving or rejecting service for a UEby femtocell system 450. Additionally, femtocell system 450 includes anInternet Operating System (IOS) and SIP Adapter (collectively referredto as IOS-SIP Adapter 440). IOS-SIP adapter 440 may invoke and manageSIP clients, such as a user agent (UA) pool comprising one or more UAs.Each UE 325 authorized to be serviced by femtocell system 450 may have aUA allocated therefor by femtocell system 450 in a manner thatfacilitates transmission of communications to and from a UE over an IPbackhaul. Accordingly, when an authorized UE is within the femtocellsystem 450 site range, telecommunication services may be provided to theUE via the IP backhaul and the femtocell system 450 provisioned RAN.When the UE is moved beyond the service range of femtocell system 450,telecommunication service may then be provided to the UE viamacrocellular coverage. Femtocell system 450 may perform a DNS/ENUMregistration on behalf of UEs authorized to obtain service fromfemtocell system 450 and may generate and issue a SIP registration onbehalf of a UE authorized for service access by the femtocell system 450in a manner similar to that described above with reference to femtocellsystem 350.

FIG. 5 is a diagrammatic representation of an exemplary SIP registrationmessage 500 generated by femtocell system 350 on behalf of UE 325authorized for service access thereby in accordance with an embodiment.Registration message 500 may be transmitted from femtocell system 350 toa location service, such as a SIP registrar implemented as SIP Registrar380. Registrar 380 may provide the location and contact information tolocation service 382. Registration message 500 includes a REGISTER field510 that specifies the registration is being made within the domain“example.com”. In accordance with an embodiment, multiple contacts areincluded in registration message 500. In the present example,registration message 500 includes a contact field 512 that specifies aSIP contact for UE 325. Notably, the SIP contact field 512 for UE 325specifies the UA registered on behalf of UE with the URI12145551212@exmaple.com is located at the IP address of “66.249.73.42”.That is, the SIP contact registered by femtocell system 350 on behalf ofUE 325 is to be addressed at the femtocell system 350 address of66.249.73.42 thereby resulting in routing of SIP signaling messages tofemtocell system 325. In turn, femtocell system 350 may convert SIP callset up messaging to RAN signaling, allocate an uplink and a downlinkchannel for UE 325, and set up a call or data session thereon.

In the present example, registration message 500 includes a secondcontact field 514 that specifies a telephone URI, e.g., the MSISDN+1-214-555-1212 of UE 325. Thus, a location query for the SIP URIsip:12145551212@example.com would return two contacts. The first is theSIP URI that can be used to reach femtocell system 350, and thus UE 325thereby, and the second is the telephone URI that can be used to reachUE 325 via macrocellular coverage, i.e., via RAN 310. As is understood,the order of contacts 512-514 provides a contact preference, and themultiple contacts may be registered in separate registration messages.The depicted registration message including both the SIP contact URI andtelephone URI is exemplary only. Accordingly, in the present example, anattempt to contact UE 325 may first be made via the SIP URI12145551212@example.com. In the event that the session is notsuccessfully set up via the SIP contact, an attempt may be made to setupa session via RAN 310 using the telephone URI.

When the UE 325 moves outside the coverage area of femtocell system 350,another registration may be generated and submitted by femtocell system350 on behalf of UE 325 where the telephone URI is designated as thepreferred contact. Further, the SIP URI may be removed from theregistration when the UE 325 moves outside the coverage area offemtocell system 350 thereby avoiding any attempts to establish asession with UE 325 via femtocell system 350 when UE 325 has movedbeyond the femtocell system 350 coverage area.

To better facilitate an understanding of disclosed embodiments, considera call placed at circuit switched telephone 332 to UE 325. A gatewayreceives the call setup request, e.g., an Initial Address Message (IAM),and a query may be made with DNS 372 from which the domain “example.com”is resolved from the ENUM function. An INVITE message is thentransmitted to the example.com domain which, in turn, resolves thelocation of the called UE 325. Particularly, CSCF 320 may interrogatelocation server 382 and determine UE 325 is registered as located at theIP address 66.249.73.42. Accordingly, the INVITE message is routed toproxy server 376 which forwards the INVITE message to femtocell system350. Femtocell system 350 may then perform paging, channel allocation,and other procedures for provisioning a radio interface with UE 325 andissue SIP responses on behalf of UE 325. Thus, from a networkperspective, femtocell system 350 appears as a user agent to which thecall is directed. Further, UE 325 does not require a SIP client forreceiving the call because femtocell system 350 advantageously performssignaling and media conversion for signaling and media transmissionsover the air interface with 325. Thus, femtocell system 350 may appearas a conventional BTS to UE 325. A call from UE 325 to another terminal,such as circuit-switched telephone 332, a SIP client such aspacket-switched telephony device 374 a, or another device, may similarlybe facilitated by femtocell system 350.

As a second example, assume UE 325 has moved beyond the range offemtocell system 350. As noted above, femtocell system 350 may generateand transmit a registration message that excludes the SIP contact tofacilitate provisioning of telecommunication services via macrocellcoverage, e.g., via RAN 310. For instance, femtocell system 350 mayperiodically perform power measurements with UE 325, and upon the powermeasurement dropping below a particular power threshold, femtocellsystem may determine UE 325 is to be serviced by macrocellular coverage.Alternatively, a user may select macrocellular coverage via a userinterface provided on UE 325. In this instance, UE 325 may provide anindication to femtocell system 350 that telecommunication services areto be provided by RAN 310. Other scenarios may similarly result in adetermination that UE 325 is to be serviced by RAN 310. Upon such adetermination, femtocell system 350 may generate and transmit aregistration message on behalf of UE 325 to a registrar service, e.g.,CSCF 320 and SIP registrar 380. The contact information may then beupdated in location server 382 to indicate the telephone URI as thecontact of UE 325. In this scenario, consider a call placed at circuitswitched telephone 332 to UE 325. A gateway receives the call setuprequest, e.g., an Initial Address Message (IAM), and a query may be madewith DNS server 372 from which the domain “example.com” is resolved fromthe ENUM service. An INVITE message is then transmitted to theexample.com domain which resolves the location of called UE 325. In thepresent example, CSCF 320 may interrogate location server 382 anddetermine UE 325 has a preferred contact registered as a telephone URIof 2145551212. Accordingly, the INVITE message is routed to a gatewayserver, e.g., gateway server 390 which translates the INVITE message toa RAN-compliant call request signaling. The call may then be setup viaRAN 310 accordingly.

In accordance with an embodiment, a network of femtocell systems may bedeployed and connected with an IP backhaul. In this implementation, anauthorized UE may be serviced by the femtocell network, and service maybe transferred from one femtocell to another femtocell via a femtocellhandoff procedure. In the event that the femtocell network is deployedin an area serviced by a macrocellular network, handoff routines mayprovide preference for transferring a UE to a target femtocell systemrather than a macrocell site. In the event that a suitable femtocell isunavailable for handoff of a UE, the UE may be transferred to themacrocell site.

FIG. 6 is a diagrammatic representation of a network system 600featuring a femtocell network implemented in accordance with anembodiment of the invention. System 600 includes a RAN 610 that providesan over-the-air interface with a UE 625, e.g., a mobile terminal. RAN610 may comprise, for example, a CDMA radio access network or anothersuitable RAN. RAN 610 may comprise various BTSs 612 a-612 c andassociated BSCs 604 as well as other infrastructure as is understood.Each of BTSs 612 a-612 c provide a respective macrocell 602 a-602 c thatmay provide telecommunication service to UE 625. BSC 604 is coupled witha MSC 606 that provides cellular exchange services, mobility management,and other services within the area that it serves as is understood.

RAN 610 may interface with IMS 620 adapted to provide IP service to UE625. To this end, RAN 610 may be communicatively coupled with a SGSN 614and a GGSN 616. GGSN 616 is communicatively coupled with a PDF 618 thatprovides authorization of media plane resources. PDF 618 may becommunicatively coupled with a CSCF 620.

CSCF 620 comprises various SIP servers or proxies that process SIPsignaling packets in IMS 620. CSCF 620 may include a P-CSCF, a S-CSCF,and an I-CSCF as is understood. HSS 640 stores user profiles thatspecify subscription-related information of authorized users,authenticates and authorizes users, and provides information about theuser's physical location. Various application servers 642 a-642 n mayhost and execute services and is interfaced with CSCF 620 via SIP.

CSCF 620 is coupled with a BGCF 622 that comprises a SIP server thatprovides routing functionality based on telephone numbers. A MGCF 624performs call control protocol conversion between SIP and ISDN User Part(ISUP) and interfaces with a SGW 626 that itself interfaces with thesignaling plane of a circuit switched network, e.g., PSTN 630. A MGW 628interfaces with the media plane of PSTN 630 or another circuit switchednetwork. Resources of MGW 628 are controlled by MGCF 624. Fixed accessdevices, e.g., IP telephony devices 674 a-674 b, may connect with IMSnetwork via Internet 670 that is communicatively coupled with IMSnetwork 620 by way of border gateway 660.

Femtocell systems 650 a-650 c may include integrated BTS and BSCfunctions and may feature additional capabilities available in theprovided femtocell site coverage areas. Femtocell systems 650 a-650 cprovide an IP-accessible radio access network, are adapted for operationwith IMS 620, and provide radio link control functions. Femtocellsystems 650 a-650 c may be communicatively coupled with Internet 670 viaany variety of backhaul technologies, such as an 802.11x link, a 10/100BaseT LAN link, a T1/E1 Span or fiber, cable set top box, DSL modemconnected with a central office digital subscriber line accessmultiplexer, a very small aperture terminal (VSAT), or another suitablebackhaul infrastructure. In the illustrative example, femtocell systems650 a-650 c are each coupled with an IP backhaul access device 655, suchas an Ethernet cable or DSL router. For instance, femtocell systems 650a-650 c may be coupled with access node 655 via respective 10/100BaseTtwisted pair cables, Category 5 cabling, or other suitableinterconnection.

Each of femtocell systems 650 a-650 c provide a respective femtocellsite 651 a-651 c in which UE 625 may be provided telecommunicationservices over an air interface. Femtocell systems 650 a-650 c arecommunicatively coupled with one another via access device 655.Femtocells 650 a-650 c deployed for conjunctively providing a femtocellservice coverage area comprised of the collective femtocell sites 651a-651 c are collectively referred to herein as a femtocell network. Inan embodiment, femtocell systems 650 a-650 c may exchange messages withone another to facilitate handoff of a UE from one femtocell to another,e.g., as UE 625 moves out of the radio range of a femtocell and into theradio range of another. In the depicted example, the femtocell networkprovided by femtocell systems 650 a-650 c is at least partiallyoverlapped by one or more macrocell sites 602 a-602 c provisioned bymacrocell BTSs 612 a-612 c. In such an implementation, femtocell systems650 a-650 c may provide preference to another femtocell for handoff of aUE thereto. In the event that another femtocell is not available or isunsuitable for a handoff, the UE may then be transferred tomacrocellular coverage via a handoff to a macrocell BTS.

In an embodiment, each of femtocell system 650 a-650 c include arespective SIP adapter that supports a SIP client pool and providesconversion of call set-up functions to SIP client set-up functions.Additionally, femtocell systems 650 a-650 c include ESN and/or MEIDscreening to allow only designated UEs to access the femtocells therebyrestricting access to authorized home or small office UEs. Provisioningof ESN(s) or MEID(s) may be made as part of an initial femtocell systemactivation. In the illustrative example, femtocell systems 650 a-650 care allocated a respective IP address of“66.249.73.42”, “66.249.73.43”,and “66.249.73.44”, and UE 625 is allocated a MSISDN number, or E.164number, of “12145551212”.

Various power measurements may periodically be made by femtocell systems650 a-650 c to monitor the communication link quality between afemtocell system and a UE. In the event that a link quality falls belowa particular threshold, a handoff procedure may be invoked to transferthe UE to another femtocell system exhibiting a better radio interfacequality with the UE, e.g., when the UE is moving away from one femtocellsystem and is reaching the periphery of the femtocell system's rangewhile concurrently moving into another femtocell system's range. Forexample, femtocell systems 650 a-650 c may measure the pilot strength,e.g., the ratio of received pilot energy, Ec, to total received energyor the total power spectral density, Io, (the ratio commonly referred toas Ec/Io) in the pilot channel, such as the common pilot channel(CPICH). If the Ec/Io measurement falls below a predefined handoffthreshold, the femtocell system may then attempt to identify a suitablefemtocell system candidate for handoff of the UE. UEs may likewiseperform power or link quality measurements, and in the event the poweror link quality falls below a predefined threshold, the UE may issue arequest to the source or servicing femtocell system for a handoff toanother cell. For instance, a UE may periodically measure the ReceivedSignal Code Power (RSCP), and request the source femtocell systemperform a handoff if the measured RSCP falls below a predefinedthreshold.

In accordance with an embodiment, femtocell systems 650 a-650 c deployedin a network of femtocell systems may periodically transmit powermeasurements or other link quality metrics to other femtocell systems.Accordingly, if a source femtocell system determines a handoff should beperformed, the source femtocell system may evaluate the most recentpower measurements of other femtocell systems to identify a suitablecandidate for handoff. In a similar manner, if a source femtocell systemreceives a request for handoff from a UE, the source femtocell systemmay evaluate the power measurement or other link quality metrics ofother femtocell systems to identify a suitable candidate for handoff.

FIG. 7 is a flowchart 700 depicting a handoff routine that facilitateshandoff of a UE from one femtocell system to another femtocell system inaccordance with an embodiment. The processing steps of FIG. 7 may beimplemented as computer-executable instructions processed by a sourcefemtocell system currently servicing a UE and that may handoff a UE toanother femtocell system. As referred to herein, a cell, e.g., providedby a femtocell system or a macrocellular system, to which a UE istransferred as the result of a handoff procedure is referred to as thetarget cell.

The handoff routine is invoked (step 702), and a link quality, such asEc/Io, associated with a UE serviced by the femtocell system may becompared to a quality threshold (step 704). If the link quality is notless than the quality threshold thereby indicating a handoff is notrequired, the handoff routine cycle may then end (step 720). If the linkquality is determined to be less than a quality threshold, the mostrecent link quality measurements received from other femtocell systemsare read (step 706). An evaluation may then be made to determine if anyof the link quality measurements of the candidate femtocell systemsindicate a suitable candidate for handoff (step 708). If a suitablefemtocell system candidate is not identified, a handoff to a macrocellsite may then be made (step 710)—the implementation of which is outsidethe scope of the present disclosure. The handoff routine may then endaccording to step 720.

If a suitable femtocell candidate is identified for handoff at step 708,a handoff request may then be transmitted to the identified femtocellsystem (step 712). An evaluation may then be made to determine if theidentified target femtocell system has accepted the handoff request(step 714). If the identified target femtocell system does not acceptthe handoff request, an evaluation may then be made to determine ifanother femtocell system is suitable for a handoff (step 716). If noadditional femtocell system is suitable for a handoff, a handoff maythen be made to a macrocell site (if available) according to step 710).If another femtocell system is identified as a suitable target femtocellsystem at step 716, a request for handoff may be transmitted to theidentified femtocell system according to step 712.

Returning again to step 714, if the identified target femtocell systemaccepts the handoff request, handoff of the UE may then be completedwith the target femtocell system (step 718), and the handoff routinecycle may then end according to step 720.

FIG. 8 is a flowchart 800 depicting a handoff routine that facilitateshandoff of a UE from one femtocell system to another femtocell system inaccordance with an embodiment. The processing steps of FIG. 8 may beimplemented as computer-executable instructions processed by a targetfemtocell system to which a UE may be transferred as the result of ahandoff procedure.

The handoff routine is invoked (step 802), and a handoff notificationmay be received from a source femtocell system currently servicing a UEfor which a handoff is to be performed (step 804). The target femtocellsystem may then evaluate whether the femtocell system has availablecapacity to complete the handoff (step 806). If the target femtocellsystem does not have suitable capacity for transfer of the UE thereto, ahandoff denial notification may be transmitted to the source femtocellsystem (step 808), and the handoff routine cycle may then end (step820).

Returning again to step 806, if the target femtocell system has suitablecapacity to complete the handoff, a handoff confirmation may betransmitted from the target femtocell system to the source femtocellsystem (step 810). The target femtocell system may then optionallyallocate a forward and reverse channel for the UE to be transferredthereto (assuming the handoff is an active handoff) (step 812), and auser agent may be allocated by the target femtocell system for the UE(step 814). A registration for the UE may then be submitted on behalf ofthe UE (step 816). The registration may include the IP address of thetarget femtocell system as the preferred or current contact of the UE.The handoff process is then completed (step 818), and the routine cyclemay then end according to step 820.

As an example, assume UE 625 is registered with femtocell system 650 aand has moved to the periphery of femtocell site 651 a. Femtocell system650 a periodically measures a link quality with UE 625. Additionally,femtocell system 650 a may receive power measurements, such as Ec/Iomeasurements, from at least a subset, e.g., neighbor femtocells, offemtocell systems 650 b-650 c commonly deployed in the femtocell networkwith femtocell system 650 a. In an embodiment, each of femtocell systems650 a-650 c may maintain a neighbors list that comprises a list ofpotential target femtocells for a handoff when it is necessary totransfer coverage of UE 625 to another femtocell. In thisimplementation, each femtocell configured as a neighbor of anotherfemtocell may periodically transmit a power measurement to any femtocellhaving the particular femtocell listed as a neighbor. In the presentexample, assume femtocell system 650 b is the only femtocell listed as aneighbor and the only femtocell that transmits power measurements tofemtocell system 650 a. Further assume that the power measured byfemtocell system 650 a with UE 625 is determined to be less than aquality threshold that indicates a minimum link quality for maintainingservice by femtocell system 650 a. In this instance, femtocell system650 may evaluate the most recent power measured or other link qualitymetric of neighbor femtocell system 650 b to determine if femtocellsystem 650 b is a suitable handoff candidate according to step 708 ofFIG. 7. Assume for illustrative purposes that the power measurementindicates femtocell system 650 b is a suitable candidate for handoff ofUE 625. Accordingly, femtocell system 650 a may transit a handoffrequest to femtocell system 650 b according to step 712. Assume thatfemtocell system 650 b accepts the handoff request according to step810. On receipt of the handoff confirmation, femtocell system 650 a maycomplete the handoff with femtocell system 650 b. To this end, femtocellsystem 650 b may allocate a forward and reverse link for UE 625 in theevent that the handoff is an active handoff according to step 812, i.e.,UE 625 is currently engaged in a call or data session. Additionally,femtocell system 650 b may allocate a SIP user agent for UE 625 andsubmit a registration message to a location service on behalf of UE 625according to steps 814 and 816 of FIG. 8. For example, femtocell system650 b may generate a SIP registration message similar to the exemplaryregistration message 900 depicted in FIG. 9. Notably, registrationmessage 900 submitted by target femtocell system 650 b on behalf of UE625 to be transferred thereto includes a contact field 910 thatspecifies the IP address (66.249.73.43 in the present example) offemtocell system 650 b as a contact for UE 625.

As described, a communication system featuring an IP-based femtocellnetwork for provisioning communication services to a user equipment isprovided. An authorized UE may be serviced by the femtocell network, andservice may be transferred from one femtocell to another femtocell via afemtocell handoff procedure. Femtocell systems of the femtocell networkperform link quality measurements and may distribute the link qualitymeasurements to neighbor femtocells. A femtocell system with which auser equipment is registered may periodically evaluate the link qualitywith the user equipment. If an evaluation is made that the userequipment needs to be transferred to another site, the servicingfemtocell site may evaluate the most recent link quality measurementsreceived from neighboring femtocell sites and select a femtocell sitefor handoff. In the event that the femtocell network is deployed in anarea serviced by a macrocellular network, handoff routines may providepreference for transferring the user equipment to a target femtocellsystem rather than a macrocell site. In the event that a suitablefemtocell is unavailable for handoff of the user equipment, the userequipment may be transferred to the macrocell site.

The flowcharts of FIGS. 7-8 depict process serialization to facilitatean understanding of disclosed embodiments and are not necessarilyindicative of the serialization of the operations being performed. Invarious embodiments, the processing steps described in FIGS. 7-8 may beperformed in varying order, and one or more depicted steps may beperformed in parallel with other steps. Additionally, execution of someprocessing steps of FIGS. 7-8 may be excluded without departing fromembodiments disclosed herein.

The illustrative block diagrams depict process steps or blocks that mayrepresent modules, segments, or portions of code that include one ormore executable instructions for implementing specific logical functionsor steps in the process. Although the particular examples illustratespecific process steps or procedures, many alternative implementationsare possible and may be made by simple design choice. Some process stepsmay be executed in different order from the specific description hereinbased on, for example, considerations of function, purpose, conformanceto standard, legacy structure, user interface design, and the like.

Aspects of the present invention may be implemented in software,hardware, firmware, or a combination thereof. The various elements ofthe system, either individually or in combination, may be implemented asa computer program product tangibly embodied in a machine-readablestorage device for execution by a processing unit. Various steps ofembodiments of the invention may be performed by a computer processorexecuting a program tangibly embodied on a computer-readable medium toperform functions by operating on input and generating output. Thecomputer-readable medium may be, for example, a memory, a transportablemedium such as a compact disk, a floppy disk, or a diskette, such that acomputer program embodying the aspects of the present invention can beloaded onto a computer. The computer program is not limited to anyparticular embodiment, and may, for example, be implemented in anoperating system, application program, foreground or background process,driver, network stack, or any combination thereof, executing on a singleprocessor or multiple processors. Additionally, various steps ofembodiments of the invention may provide one or more data structuresgenerated, produced, received, or otherwise implemented on acomputer-readable medium, such as a memory.

Although embodiments of the present invention have been illustrated inthe accompanied drawings and described in the foregoing description, itwill be understood that the invention is not limited to the embodimentsdisclosed, but is capable of numerous rearrangements, modifications, andsubstitutions without departing from the spirit of the invention as setforth and defined by the following claims. For example, the capabilitiesof the invention can be performed fully and/or partially by one or moreof the blocks, modules, processors or memories. Also, these capabilitiesmay be performed in the current manner or in a distributed manner andon, or via, any device able to provide and/or receive information.Further, although depicted in a particular manner, various modules orblocks may be repositioned without departing from the scope of thecurrent invention. Still further, although depicted in a particularmanner, a greater or lesser number of modules and connections can beutilized with the present invention in order to accomplish the presentinvention, to provide additional known features to the presentinvention, and/or to make the present invention more efficient. Also,the information sent between various modules can be sent between themodules via at least one of a data network, the Internet, an InternetProtocol network, a wireless source, and a wired source and viaplurality of protocols.

What is claimed is:
 1. A method, comprising: measuring a first radiointerface quality between a user equipment and a first femtocell;measuring a second radio interface quality between the user equipmentand a second femtocell; transmitting an indication of the second radiointerface quality from the second femtocell to the first femtocell; andinvoking a handoff procedure from the first femtocell to the secondfemtocell; wherein the first femtocell and the second femtocell areconnected to an internet via a same internet access device, wherein theinternet access device is a packet-switched backhaul, wherein the firstfemtocell and the second femtocell communicate with one another via thepacket-switched backhaul without communicating via the internet, andwherein each of the first femtocell and the second femtocell include arespective integrated base station controller, base transceiver stationand Session Initiation Protocol (SIP) adapter that supports a SIP clientpool and provides conversion of call set-up functions to SIP clientset-up functions.
 2. The method of claim 1, further comprising:determining, by the first femtocell, that the first radio interfacequality is below a predefined quality threshold; and determining, by thefirst femtocell, that the second radio interface quality is sufficientfor the handoff.
 3. The method of claim 1, further comprising:transmitting, by the first femtocell, a request for handoff to thesecond femtocell; and receiving, by the first femtocell, a responseaccepting the handoff from the second femtocell.
 4. The method of claim1, further comprising allocating, by the second femtocell, a user agentfor the user equipment.
 5. The method of claim 4, further comprisingtransmitting, by the second femtocell, a registration message to alocation service on behalf of the user equipment, wherein theregistration message includes an Internet Protocol address assigned tothe second femtocell as a contact for the user equipment.
 6. The methodof claim 5, further comprising: receiving the registration message bythe location service; and updating, by the location service, a locationassociated with the user equipment that specifies an Internet Protocoladdress assigned to the first femtocell to the Internet Protocol addressassigned to the second femtocell.
 7. The method of claim 1, furthercomprising maintaining, by the first femtocell, radio interface qualitymeasurements for evaluation of a candidate femtocell for handoff whenthe first radio interface quality is determined to be less than aquality threshold.
 8. The method of claim 1, wherein measuring the firstradio interface quality is performed by the user equipment, the methodfurther comprising transmitting, by the user equipment, a request forhandoff to the first femtocell.
 9. A non-transitory computer-readablemedium having computer-executable instructions for execution by aprocessing system, the computer-executable instructions for: measuring afirst radio interface quality between a user equipment and a firstfemtocell; measuring a second radio interface quality between the userequipment and a second femtocell; transmitting an indication of thesecond radio interface quality from the second femtocell to the firstfemtocell; and invoking a handoff procedure from the first femtocell tothe second femtocell; wherein the first femtocell and the secondfemtocell are connected to an internet via a same internet accessdevice, wherein the internet access device is a packet-switchedbackhaul, wherein the first femtocell and the second femtocellcommunicate with one another via the packet-switched backhaul withoutcommunicating via the internet, and wherein each of the first femtocelland the second femtocell include a respective integrated base stationcontroller, base transceiver station and Session Initiation Protocol(SIP) adapter that supports a SIP client pool and provides conversion ofcall set-up functions to SIP client set-up functions.
 10. Thenon-transitory computer-readable medium of claim 9, further comprisinginstructions for: determining, by the first femtocell, that the firstradio interface quality is below a predefined quality threshold; anddetermining, by the first femtocell, that the second radio interfacequality is sufficient for the handoff.
 11. The non-transitorycomputer-readable medium of claim 9, further comprising instructionsfor: transmitting, by the first femtocell, a request for handoff to thesecond femtocell; and receiving, by the first femtocell, a responseaccepting the handoff from the second femtocell.
 12. The non-transitorycomputer-readable medium of claim 11, further comprising instructionsfor transmitting, by the second femtocell, a registration message to alocation service on behalf of the user equipment, wherein theregistration message includes an Internet Protocol address assigned tothe second femtocell as a contact for the user equipment.
 13. Thenon-transitory computer-readable medium of claim 12, further comprisinginstructions for: receiving the registration message by the locationservice; and updating, by the location service, a location associatedwith the user equipment that specifies an Internet Protocol addressassigned to the first femtocell to the Internet Protocol addressassigned to the second femtocell.
 14. The non-transitorycomputer-readable medium of claim 9, further comparing instructions formaintaining, by the first femtocell, radio interface qualitymeasurements respectively obtained by at least a subset of the pluralityof femtocells for evaluation of a candidate femtocell for handoff whenthe first radio interface quality is determined to be less than aquality threshold.
 15. The non-transitory computer-readable medium ofclaim 9, wherein measuring the first radio interface quality isperformed by the user equipment, the method further comprisingtransmitting, by the user equipment, a request for handoff to the firstfemtocell.
 16. A system, comprising: a packet-switched network withwhich a user equipment has a session initiation protocol servicesubscription; an Internet Protocol multimedia subsystem communicativelyinterfaced with the packet-switched network; and a femtocell networkincluding a first femtocell and a second femtocell, wherein thefemtocell network: measures a second radio interface quality between theuser equipment and a second femtocell; transmits an indication of thesecond radio interface quality from the second femtocell to the firstfemtocell; and invokes a handoff procedure from the first femtocell tothe second femtocell; wherein the first femtocell and the secondfemtocell are connected to an internet via a same internet accessdevice, wherein the internet access device is a packet-switchedbackhaul, wherein the first femtocell and the second femtocellcommunicate with one another via the packet-switched backhaul withoutcommunication via the internet, and wherein each of the first femtocelland the second femtocell include a respective integrated base stationcontroller, base transceiver station and Session Initiation Protocol(SIP) adapter that supports a SIP client pool and provides conversion ofcall set-up functions to SIP client set-up functions.
 17. The system ofclaim 16, wherein the first femtocell determines that the first radiointerface quality is below a predefined quality threshold and determinesthat the second radio interface quality is sufficient for the handoff.18. The system of claim 16, wherein the first femtocell transmits arequest for handoff to the second femtocell and receives a response thataccepts the handoff from the second femtocell.
 19. The system of claim16, wherein the second femtocell submits a registration message to alocation service on behalf of the user equipment, wherein theregistration message includes an Internet Protocol address assigned tothe second femtocell as a contact for the user equipment.
 20. The systemof claim 19, wherein the location service receives the registrationmessage and updates a location associated with the user equipment thatspecifies an Internet Protocol address assigned with the first femtocellto the Internet Protocol address assigned to the second femtocell.